HEPA Filters for SLD Ceiling Systems

NOTICE: General Reference Only

The information provided in this article is for general reference purposes only and does not constitute project-specific guidance. SLD Technology products are engineered to order, and their installation must comply with all applicable codes, standards, and project-specific specifications. In all cases, the approved project documentation and requirements take precedence over any general information contained herein. For project-specific instructions, contact your SLD Project Manager or the SLD Product Support team at: support@sldus.com.

Summary

This article explains what a HEPA filter is, where HEPA filtration is located in a healthcare air system (air handler versus terminal/ceiling grid), and how HEPA filters for SLD system projects are ordered, shipped, received, inspected, stored, and installed.

The guidance in this article is provided as general reference information. Filter selection, installation, testing, monitoring, and replacement are the responsibility of the Owner, the mechanical contractor, or their qualified personnel and fall outside SLD Technology's scope of supply. Follow your facility's own procedures, the filter manufacturer's instructions, the project's contract documents, and any applicable code or cleanroom protocols, and consult a qualified professional for your specific installation.

What is a HEPA filter?

HEPA stands for High Efficiency Particulate Air (sometimes referred to as High Efficiency Particulate Arrestance or Arresting). A HEPA filter is a mechanical filter built from a densely pleated media pack (typically glass fiber) held in a rigid frame and sealed to the frame so that all air must pass through the media rather than around it.

To be classified as HEPA, a filter must remove at least 99.97% of particles at 0.3 micron at its rated airflow, when tested in accordance with IEST-RP-CC001. The 0.3 micron size is used as the rating point because it is the most penetrating particle size — the size that is hardest for the media to capture. Particles both larger and smaller than 0.3 micron are actually captured at higher efficiency, so a 99.97% rating at 0.3 micron represents the filter's worst-case performance, not its typical performance.

A few points that commonly cause confusion:

HEPA is not a MERV rating. MERV (from ASHRAE Standard 52.2) tops out at MERV 16. HEPA filtration is a separate, higher classification and is not expressed as a MERV number.
HEPA filters are not the first line of defense. They are the final stage in a multi-stage filter train. Upstream prefilters remove the bulk of the particulate load and exist specifically to protect the HEPA filter and extend its service life.

Where are HEPA filters located?

HEPA filtration is generally located at one of two locations: At the air handler unit (AHU) or at the air terminal device (the grid face, right before air enters the room).

The location of HEPA filtration can be dictated by code; however, it is most commonly a discretionary decision made by project teams like yours. As with any construction project, decisions are made based on many factors such as: Status quo ("this is how we have always done it"), code compliance, best practices, budget, etc. HEPA filter placement is no different.

Status quo puts HEPA filters at the AHU. Recent ASHRAE revisions require HEPA filters at the air terminal device for certain rooms seeing certain cases, and most Authorities Having Jurisdiction (AHJs) enforce those provisions as strict requirements.

SLD ceiling systems including AirFRAME®, AirFRAME-LT®, and LEDiffuser® are manufactured HEPA-ready unless otherwise specified in the project documentation.

	Air handler unit (AHU)	Air terminal device
Location	Filter bank at the AHU, upstream of the supply ductwork	At the ceiling grid face, immediately before air enters the room
Air path after filtration	Travels the full duct run before reaching the room	Enters the room directly
Serves	Every space on that air handler	One room
Typical filter format	Deep-bed / V-bank cells, high face velocity	Large-area gel-seal panels across a diffuser array, low face velocity
Verification at the room	Not practical	Possible; can be scan-tested at the room face

At the air handler unit (AHU)

This is the traditional placement and remains the most common. It is not a wrong approach. The air genuinely is filtered to HEPA efficiency, and there are real reasons teams choose it:

One filter bank serves every space on the unit, so there are fewer filters to track
Filter changes happen in a mechanical room instead of in a clinical space
It is familiar to designers, contractors, and facilities staff
It carries a lower initial cost on the filter line item

The limitations come from where the filter sits relative to the room:

Everything downstream of the filter is an unfiltered path. Air leaves the filter clean, then travels the entire duct run before reaching the patient. Anything the duct contributes along the way is delivered to the room: construction debris left at turnover, flaking duct liner, mold at a condensation point, or rodent intrusion. In an operating room that air is delivered as a downward flow directly over an open surgical site.
Shorter filter life and higher operating cost. A compact filter bank handling the full unit airflow runs at high face velocity, which loads the media faster and drives a higher pressure drop.
Higher static pressure penalty across the whole system. That resistance applies to every space on the unit, including spaces that do not need HEPA-quality air.
No practical way to verify performance at the room. A filter that tests clean at the AHU tells you nothing about what is actually arriving at the ceiling.
Filter changes affect every room on the unit at once, rather than one room at a time.

At the air terminal device (ceiling grid, just before entering room)

Here, the HEPA filter is the last thing the air touches before it enters the room. The duct run, whatever condition it is in, sits upstream of the filter rather than downstream of it. Filtration happens at the last possible moment, at the point where it protects the patient the most.

This placement also produces a longer-lasting filter, a lower static pressure burden on the air handler, room-by-room serviceability, and the ability to actually verify the installation from inside the room.

Code requirements

Under ANSI/ASHRAE/ASHE Standard 170-2021 (Ventilation of Health Care Facilities), operating rooms require a minimum final filter efficiency of MERV 16. Beyond that baseline, Section 7.4.1(c) requires that HEPA filters be provided and located in the air terminal device for operating rooms or Class 3 imaging rooms designated for:

Orthopedic procedures
Transplants
Neurosurgery
Dedicated burn unit procedures

An errata published by ASHRAE in May 2024 clarified this requirement: the air system for these spaces is not required to carry two sets of HEPA filters. Only one set is required, and it must be located at the terminal end, just before air enters the room.

NOTE: Local Codes Supersedes

Standard 170 is periodically revised and is adopted, amended, or superseded differently by different AHJ, including outside the United States. Always confirm the edition and any local amendments enforced on your project with the design engineer of record and the AHJ. Nothing in this article substitutes for the project's contract documents.

What types of filters are available?

SLD Technology offers HEPA filters in two media types: Glass fiber media and PTFE membrane media. Both meet HEPA efficiency requirements; the difference is in the media construction, durability, and cost. Filters are sourced from established filtration manufacturers and are sized to the AirFRAME®, AirFRAME-LT®, or LEDiffuser® array for the specific project and system size. Dimensions vary by project, and are confirmed during the submittal process with your SLD Project Manager.

Glass Fiber Media

Glass fiber has been the standard HEPA media for decades and is what SLD Technology has historically supplied.

Proven, well-understood performance with a long track record in healthcare
Fragile. Media pack is easily damaged by contact, pressure, or flexing of the frame
Not tolerant of moisture. A wetted glass fiber filter should be considered compromised and replaced
Fibers can shed if damaged

PTFE Membrane Media

PTFE (polytetrafluoroethylene) membrane is a newer media technology that achieves HEPA efficiency through an expanded membrane structure rather than a glass fiber matrix.

Significantly more durable. The membrane is far more resistant to physical handling damage than glass fiber.
Moisture tolerant. PTFE is hydrophobic and does not absorb water the way glass fiber does, which makes the filter far more forgiving of humidity, condensation, and incidental wetting.
Cleanable surface. Depending on the specific product and its manufacturer's instructions, the filter face can tolerate wiping or washing that would destroy a glass fiber filter.
Lower pressure drop for equivalent efficiency in most configurations, which reduces fan energy and can extend service life
No fiber shedding and no boron content

What size filters do I need?

HEPA filters are sized to the SLD system. They are not an off-the-shelf item

An SLD Technology system is an array of several differently sized openings together forming a Single Large Diffuser. While those opening sizes are often standard to SLD, they do not correspond to standard filter sizes in the filtration industry. A filter ordered against a nominal industry size will not fit an SLD opening.

WARNING: Filters Must Be Sized to the SLD System

SLD opening sizes and knife edge geometry do not correspond to standard filter sizes in the filtration industry. A filter ordered against a nominal industry size will not fit, and a filter that does not seat correctly creates a bypass path around the media. Air then enters the room without passing through the filter, and its efficiency rating becomes meaningless.

Never order replacement filters from field measurements or a manufacturer's standard size chart. Order through SLD Technology, or coordinate filter frame and knife edge dimensions through SLD before placing the order elsewhere.

Ordering process and lead time

HEPA filters ship separately from the ceiling system

HEPA filters supplied by SLD on an SLD project are drop-shipped directly from the filter manufacturer to the job site. They do not ship with the ceiling system and they do not pass through SLD Technology's facility.

This means:

The filters arrive on a separate shipment, under a separate BOL, from a different origin point.
The filters arrive later than the ceiling system, by design.
The receiving party on site should expect two distinct deliveries and should not assume the project is short-shipped when filters are not on the ceiling system truck.
Filters are project-specific and are not an off-the-shelf item. Filter sizes and knife edge dimensions are matched to the SLD system and do not correspond to standard industry filter sizes.

Why filters are ordered later

There is an intentional delay between when the SLD system is installed and when the HEPA filters go in. HEPA filters are the last item installed in the room. After the ceiling system is set, after the ductwork is connected, after the room is sealed, and after the space is clean.

Installing HEPA filters too early exposes them to:

Airborne construction dust from drywall, grinding, and finishing work
Duct blow-out and system startup debris
Air balancing performed before the space is clean
Physical damage from other trades working in the ceiling
Moisture and temperature swings in a building that is not yet under permanent HVAC control
Filters loaded up during construction may need to be discarded and replaced before the room is ever turned over

Ordering the filters on a schedule tied to the filter installation date, rather than the ceiling system delivery date, also limits how long they sit in storage on site, where they are exposed to handling damage and environmental risk.

Coordinate the order with your SLD Project Manager

Contact your SLD Technology Project Manager to establish the HEPA filter order date.

Your PM will work backward from the project schedule using:

The current manufacturing lead time from the filter manufacturer
Transit time to the job site
The scheduled SLD system installation and ceiling close-in dates
The anticipated date the room will be clean, sealed, and ready for filter installation
The scheduled certification/validation date

IMPORTANT NOTE: Schedule Changes Critical

Bring schedule changes to your SLD Project Manager as soon as they are known. A project that slides three months after filters have already been ordered creates a storage problem; a project that accelerates without notice creates a lead-time problem. Either one can delay room turnover.

Receiving and Inspecting HEPA filters

Inspect every shipment at the time of delivery:

At the truck

Verify the shipment against the packing list and BOL: quantity, model, size, and configuration. Confirm the filter sizes match the SLD system layout for the rooms on this project.
Photograph the load on the truck before anything is unloaded.
Inspect each pallet for:

Crushed, torn, punctured, or collapsed cartons
Leaning, shifted, or partially collapsed pallet stacks
Broken pallet stringers or deck boards
Water staining, moisture, or wet cardboard
Compromised stretch wrap or banding
Tipped or inverted pallets, or evidence that the pallets were stacked on top of one another in transit

Check any shock or tilt indicators applied to the pallets, if present.
Photograph any damage found, from multiple angles, including the pallet as a whole and the specific damage.

Noting damage

WARNING: Note Damage Before Signing

A signature with no damage notation is treated as acceptance of the shipment in good condition, and severely limits your ability to recover on a freight claim. If any damage is found, write it on the delivery receipt before you sign. Be specific: record the number of pallets or cartons affected and describe the damage. If damage is significant, refuse the affected pallets rather than accepting them.

Contact SLD Technology Product Support immediately, with photographs and the noted delivery receipt, so a freight claim can be initiated and replacement filters can be expedited.

Do not open sealed filters to inspect them

HEPA filters are packaged and sealed by the manufacturer to protect the media and keep the filter clean until installation. Leave cartons and any protective wrapping sealed until the filters are ready to be installed. Inspect the exterior packaging at receiving; the filter itself is inspected at the point of installation, immediately before it goes in.

Storage requirements

Between delivery and installation, HEPA filters must be stored in conditions that protect both the media and the frame.

Environment

Store indoors. Never store HEPA filters outdoors, in a job trailer subject to temperature extremes, in an unroofed area, or in any location exposed to weather.
Store in a cool, dry, temperature- and humidity-controlled space. Store within the temperature and humidity range specified by the filter manufacturer for the specific product supplied.
Keep filters dry. Moisture is the primary threat. Glass fiber HEPA media that has been wetted may not recover. Water can degrade the media and the sealant, and a filter that has been wet should be treated as compromised. Wet filters should not be installed.
Avoid areas with overhead piping, sprinkler risk, roof leaks, or condensation exposure.
Keep filters away from active construction. Do not store filters where drywall dust, grinding debris, welding, or painting is taking place, and do not store them in a room being used as a general staging or lay-down area.
Keep filters away from direct sunlight, exhaust fumes, and chemical vapors.

Physical handling

WARNING: Handle by the Frame, Never the Media

Fingertip pressure on the pleat pack is enough to open a leak path, and the damage often leaves no visible sign. Never touch, press, lean on, or set anything against the media. Handle filters by the frame only, and never use the frame for prying, levering, or dragging. Do not drop filters, even short distances.

Damage that goes undetected at receiving or during storage surfaces as a failed scan test later, after the filters are installed and the room is on the certification schedule.

Store on pallets or racking, off the floor. Never place cartons directly on a slab.
Follow the manufacturer's carton orientation markings. Filters are shipped in a specific orientation for a reason. Do not lay cartons flat if they are marked "this side up," and do not stand them on end if they are not marked for it.
Do not exceed the manufacturer's maximum stacking height. Do not stack other materials, tools, or equipment on top of filter cartons.
Do not double-stack pallets unless the manufacturer's packaging is explicitly rated for it.
Do not use the filter frame as a handle for prying, levering, or dragging. Do not drop filters, even short distances.
Do not remove protective packaging early, and do not remove the gasket or gel-seal protective covering until the moment of installation.

Storage duration and rotation

Store filters no longer than necessary. Extended storage increases exposure to damage, moisture, and handling.
Where filters incorporate an electret (charged) prefilter media, be aware that the electrostatic charge dissipates over time in storage as well as in service, which reduces the pre-filter's effectiveness before it is ever installed.
If multiple filter deliveries arrive on a phased project, rotate stock first-in, first-out.
Record delivery date and location so filters can be traced back to a shipment if a problem surfaces at scan testing.

Security

Store filters in a lockable or otherwise controlled area. HEPA filters are high-value items and are frequently damaged when stored in open, uncontrolled areas where other trades move material around them.

Installation timing

HEPA filters should be installed only when all of the following are true:

SLD system installation is complete and the ceiling is closed in.
Ductwork is connected, cleaned, and sealed.
Duct blow-out and initial system startup are complete.
Dust-generating construction work in and around the room is finished.
The room envelope is sealed and the space is clean.
Permanent HVAC is operating and the building is under temperature and humidity control.
A construction filter arrangement (if used during construction) is being removed at the same time.

Immediately before installation, unwrap each filter and inspect it for shipping or handling damage: creased or torn media, separation of the media pack from the frame, damage to the gasket or gel seal, a bent or racked frame, and any evidence of moisture. Contact SLD Technology Product Support immediately, with photographs, if any damage is discovered prior to or during filter installation.

After installation:

Where the project scope includes it, terminal HEPA filters should be scan-tested in place by a qualified testing agency to verify both the filter media and the frame seal. This is required on Australian projects and specified on some Canadian projects; it is less commonly specified for operating rooms in the United States.
Record the clean-filter pressure differential baseline at this time, regardless of whether scan testing is performed. Without a clean baseline there is no reference point for judging filter loading later, and the opportunity to capture it passes as soon as the room goes into service.

If you need assistance with filter installation or with anything else after the filters have arrived on site, contact SLD Technology Product Support.

Filter service life, replacement, and pressure differential monitoring

A HEPA filter does not have a fixed expiration date. Its usable life depends on how much particulate it has captured, which varies enormously between projects and even between rooms in the same facility. The practical way to judge remaining life is by measuring the pressure differential (ΔP) across the filter and comparing it to the clean-filter baseline.

For the full procedure including probe placement, penetration restrictions, sealing requirements, and how to take a valid reading, filter service life and when to change filters see the related article: Monitoring HEPA Filter Loading Through Pressure Differential.

Getting help

Situation	Contact
Filter order timing, quantities, sizes, configuration, schedule coordination before shipment	Your SLD Technology Project Manager
Shipping damage, shortages, or a discrepancy at delivery	SLD Technology Product Support
Receiving, inspection, storage, or handling questions	SLD Technology Product Support
Installation support, or anything arising after the filters are on site	SLD Technology Product Support

Contacting Support

You can reach SLD Technology Support by:

Submitting a ticket online: Click: "Submit a Ticket" at the bottom of this article or at www.sldus.com/support
Submit a ticket via Email: support@sldus.com
Phone: +1 (503) 744-0002, Option 2

All rights reserved. AirFRAME®, LEDiffuser®, uLED®, AirFRAME-LT® and associated marks are trademarks of SLD Technology, Inc. Unauthorized reproduction, distribution, or use of this manual or any portion thereof is strictly prohibited and may violate applicable laws. SLD Technology reserves the right to make changes to products, specifications, or this manual without notice. The information herein is believed to be accurate at the time of publication; however, SLD assumes no responsibility for errors, omissions, or the consequences of use.